Defaulting to "with systemd" causes problems for users who install MPD
as an unprivileged user, and it breaks "make distcheck".  It looks
like enabling it by default creates too many practical problems for
unexperienced users.

With --with-systemdsystemunitdir (without a parameter), configure.ac
attempts to auto-detect systemd.

Right now, a playlist with absolute pathnames can only add songs that
are in the same the directory of the playlist or under it.

If uri is an absolute pathname and base_uri is set,
playlist_check_translate_song() will check that base_uri is a prefix
of uri, excluding every other song in the music directory outside
base_uri.

I think in this case base_uri should be completely ignored (and made
NULL) and uri should just be checked against music root directory.

Previously, the condition "defined(play_audio_format)" was used to see
if an output device has been opened, but if the device had failed on
startup, an assertion failure could occur.  This patch adds a separate
flag.

Common function that manages "player" attributes after
audio_output_all_open() has returned.

Now that the player thread can handle SEEK commands while not (yet)
playing, we can remove the "pc.state" check from pc_seek().

This checks both conditions: pending and running.  Fixes yet another
assertion failure!

.. and add a few code comments.

Don't read song.start_ms and song.end_ms, let the player thread manage
this logic instead.

Fixes one more assertion failure.

Fixes possible assertion failure.

When playing a CUE track, the player thread waited for the decoder to
become ready, and then sent a SEEK command to the beginning of the CUE
track.  If that is near the start of the song file, and the track is
short enough, the decoder could have finished decoding already at that
point, and seeking fails.

This commit makes this initial seek more robust: instead of letting
the player thread deal with the difficult timings, let the decoder API
emulate a SEEK command, and return it to the decoder plugin, as soon
as the plugin finishes its initialization.

Wrap close(), use closesocket() on WIN32/WinSock.

Don't provide the prototype if inotify_init() was not detected.

The server_socket library (used by the httpd output plugin) didn't
check for WIN32, that's fixed now.

Allow enabling the plugin explicitly without running Solaris, to test
the build.

Wrong variable name.

The stdio header is no longer pulled in by af_vfs.h in audiofile-0.3.0.

Always lock the main loop when operating on PULSE objects.  Document
this.

Add -DNDEBUG to AM_CPPFLAGS.

Let the codec start with fresh buffers.  This should fix the remaining
seeking issues.

Use AVStream.time_base to convert the decoder_seek_where() value, and
pass the current stream number to av_seek_frame().

Use flag AV_TIME_BASE.

Code simplification.

Reduce heap usage by reducing the number of malloc() / free() calls.

D'oh, we were reading 16 bit integers instead of 32 bit integers!
That caused silence when trying to play a 32 bit input file on a 24
bit sound card (e.g. USB sound chips with 24 bit packed samples).